No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 493 
muscles arise, and along its postero-lateral edge, which is slightly 
grooved, the external rectus lies in its passage from the orbit to 
its origin, close to the middle line of the head near the hind end 
of the eye-muscle canal. In none of the specimens examined did 
the muscle arise, as stated by Sagemehl, immediately behind 
the transverse “ Wulst”’ or bar. It arises from the cartilaginous 
floor of the eye-muscle canal, or in part also from the median 
rib or ridge of the parasphenoid, which fills the median longi- 
tudinal fissure in that floor. This fissure (Zfn, Fig. 10, PI. 
XXI) is the hypophysial fenestra of Sagemehl and Wright. 
The process of the parasphenoid that fills it, although differing 
somewhat in position, may be the homologue of the one which 
in Cyprinoids is said by Sagemehl to replace the basisphenoid 
of other teleosts (No. 107, p. 575). 
In larvae of Amia, even in those 50 mm. in length, the 
internal carotid canal is represented by a foramen only which 
perforates the basal plate of the future orbital opening of the 
eye-muscle canal. The internal carotid artery, having issued 
from this foramen, runs upward and forward along the lateral 
surface of the base of the transverse cartilaginous bar of the 
chondrocranium, traversing an open space between the basal 
plate of the skull and the overhanging, upper, lateral edge of the 
bar. The anterior corner of this overhanging edge projects 
upward and forward, and the artery, having reached the anterior 
face of the bar, below and median to its projecting dorso- 
anterior corner, turns outward and upward along the dorsal 
surface of that corner, not having again entered the cartilage 
at any place. While traversing the open space along the lateral 
surface of the bar, its sends or receives a communicating 
branch from the efferent pseudobranchial artery, the branch 
giving rise, undoubtedly, to the small branch canal found in 
the basisphenoid of the adult ; though in the adult the commu- 
nicating artery itself was not traced. The three recti muscles 
which, in the adult, arise from the lateral surface of the basi- 
sphenoid, arise, in larvae, from the under surface of the dorsal 
edge of the transverse bar. The basisphenoid of Amia is 
therefore probably, in large part, a membrane bone developed in 
connection with the insertions of certain of the recti musles. 
